Situational awareness, can't preach it enough. Know who your enemy is before he realizes he is your enemy. Assess everyone in a room, or if it a crowded big room, everyone within 30 feet. Catalogue warning signs and if you assess the threat is real, start formulating a plan. If they know you have identified them, and are preparing or positioning yourself for what comes next, chances are they will pass. If not, when it starts, go on the attack, no rules, no holding back. Use whatever you have, and don't stop until the threat is completely eliminated. They are looking for something easy, not life threatening hard.
If something comes down and my wife is with me, I have one secret advantage: I know I will fight to the death to protect her, they don't. Sisco's old guy rules to live by.